1. Field of the Invention
This invention relates to a novel sulfur-containing O-(meth)acrylate compound; a process for preparation of the sulfur-containing O-(meth)acrylate compound, comprising dithioacetalization, thio-esterification or thio-urethanization of a novel thiol compound followed by dehydrohalogenation; an optical resin composition comprising the sulfur-containing O-(meth)acrylate compound; and an optical resin prepared by polymerization of the composition.
2. Description of the Related Arts
A plastic lens is lighter and less brittle than an inorganic lens, and dyeable, which has been therefore rapidly gaining prevalence in the areas of optical devices such as lenses for eyeglasses and cameras. Currently, the resins which may be widely used for these applications, include those prepared by radical polymerization of diethylene glycol bis(allylcarbonate) (referred to as `D.A.C.`). These resins have various features such as excellent impact resistance, lightness, excellent tintability, and good processability including machinability and abradability. These resins, however, have a low refractive index (n.sub.d) of about 1.50 so that it is necessary to increase the center thickness and the edge thickness, and when such requirements are met, the lens is unavoidably thickened on the whole. Therefore, a lens having a higher refractive index has been desired.
Resins with a higher refractive index than D.A.C. resin are known; for example, polythiourethane resins (e.g., JP-A 63-46213); sulfur-containing O-(meth)acrylate resins (e.g., JP-A 1-128966, 3-217412 and 4-161410); and thio(meth)-acrylate resins (e.g., JP-A 63-188660 and JP-B 3-59060), in which sulfur atoms are introduced. A polythiourethane resin is well-balanced in its properties, that is, has a high refractive index and good impact resistance and the like. When rapidly polymerizing it, the resin, however, tends to be inhomogeneously polymerized, and thus the polymerization inevitably takes longer time to obtain an optically homogeneous lens. Furthermore, during processing it by cutting and abrasion, sulfur odor may generate.
A sulfur-containing O-(meth)acrylate resin or a thio(meth)acrylate resin can be prepared by rapid polymerization by means of UV rays or the like. In general, a resin produced may, however, have inadequate strength or impact resistance, that is, it may be brittle and breakable. Recently, a resin for a lens has been required to have processing strength suitable for a two-point processing widely used in the area of a lens for eyeglasses, and a center of a lens for eyeglasses has been being thinner. Thus, there has been a demand for a resin having higher strength and impact resistance. Furthermore, since a thio(meth)acrylate compound is less stable, it may gel or tend to be uncontrollably rapidly polymerized and require complex operations. Therefore, there has been a need for further improvement to solve these problems.